Hi Hassan, I did a very simple calculation, maybe I'm wrong: an LVDS differential = swing at the driver is about 800mV and 150m of cat5 cable is about = 20-30dB of losses @30-100MHz. So at the receiver we'll have ABOUT = 80-24mV of swing, that is under or near the threshold (100mV). Are you = confident about using an LVDS with 150m of cable? In the National (DS90LV032ATM & DS90LV031ATM) appl. note 971 there is = also a picture of the signal after 10 m of cable @ 155Mb/s. Signal is = quite good, but rise and fall time increase a lot. Anyway the worst contribute to the signal in this particular case is = given by connectors, flexes and the backplane. That's why I think that the LVDS is not the FIRST choice. I think that = the noise margin could be reduced too much. Best regards, Giovanni -----Messaggio originale----- Da: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]Per conto di Hassan O. Ali Inviato: marted=EC 27 settembre 2005 16.54 A: si-list@xxxxxxxxxxxxx Oggetto: [SI-LIST] Re: R: LVDS Transmission Problem Cable loss is certainly not the problem here. Plain old LVDS signaling = can be used with=20 24 gauge twisted-pair cables even longer than 150 meters! One can refer = to the cable=20 guidelines in the LVDS standard page 25 (http://ftp.tiaonline.org/tr- 30/tr302/Public/2000%20Contributions/20005017.pdf) I think the problem here could be with the data pattern, data rate, or = the type of=20 connection. Relevant questions to consider: - Is it a dc or ac-coupled link?=20 - Does the failing data pattern have long runs of zero's and one's that = considerably=20 alter the dc balance of the signal? More so if ac-coupled. - Is 34MHz below the low frequency limit of the LVDS receiver/driver? Best regards. Hassan. On Sep 27, "Guasti Giovanni" <Giovanni.Guasti@xxxxxxxxxx> wrote: >=20 > I think LVDS is not the first choice for a so long path. > How is the measured signal? Is a problem of losses, reflections or a = =3D > signal polarization due to distributed capacitance? > maybe the LVDS suffers the high capacity of the system (maybe is just = =3D > the shield). > After the signal measurement, I would try with these: > 1)a scrambled (or a more balanced number of '1' and '0')signal=3D20 > 2)a unshielded cable / unshilded and shorter cable. > 3)replace LVDS with a LVPECL or MLVDS/BLVDS > I hope this could help you, > Giovanni >=20 >=20 > Hi=3D20 >=20 > =3D20 >=20 > We have a system which is build up two subsytem. Data signals between = =3D > the > subsystems are in LVDS format. Between these two subsystems there is = 10m > cable. LVDS data signals are carried using shielded twisted pair = cables. > Inside these two subsystem LVDS signals also passed through backplanes = =3D > and > flexes . We use national LVDS transmitter and receiver. (DS90LV032ATM = & > DS90LV031ATM) . The data rate of the LVDS signals are 34MHz. The = problem =3D > is > for some data patterns the transmitted and received data is not same? = =3D > As > the cable length is shortened to 3m and frequency of LVDS signals is > reduced the problem somewhat lowered but we have still the problem. = What > could be the reasons for this problem? >=20 > =3D20 >=20 > <mailto:r@xxxxxxxxxxxxxxxxxxx>=3D20 >=20 > M.Baris DUZGUN >=20 > Hardware Senior Expert Engineer >=20 > ASELSAN INC. MGEO Division >=20 > P.K. 30 06011 >=20 > Etlik ANKARA >=20 > TURKEY >=20 > Tel : +90 312 847 53 00 / 4534 >=20 > Fax : +90 312 847 53 20 >=20 > e-mail : bduzgun@xxxxxxxxxxxxxxxxxxx =3D > <mailto:bduzgunr@xxxxxxxxxxxxxxxxxxx>=3D20 >=20 > =3D20 >=20 >=20 We have a system which is build up two subsytem. Data =3D > =3D3D > signals > between the subsystems are in LVDS format. Between these two = subsystems =3D > =3D3D > there > is 10m cable. LVDS data signals are carried using shielded twisted = pair =3D > =3D3D > cables. > Inside these two subsystem LVDS signals also passed through backplanes = =3D > =3D3D > and flexes > . We use national LVDS transmitter and receiver. (DS90LV032ATM & > DS90LV031ATM) . The data rate of the LVDS signals are 34MHz. The = problem =3D > =3D3D > is for > some data patterns the transmitted and received data is not = same? =3D > =3D3D > As the cable > length is shortened to 3m and frequency of LVDS signals is reduced the = =3D > =3D3D > problem > somewhat lowered but we have still the problem. What could be the = =3D3D > reasons for > this problem? ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu